This invention relates to a novel two-step heat recovery submerged combustion heating system. More particularly, this invention relates to a novel submerged combustion heating system with a lowered self-cooling combustion chamber and a two-stage heat recovery system. The system can be installed singly or in combination with other similar submerged combustion systems to heat large quantities of liquids and liquid-solid solutions.
Submerged combustion heating is a method whereby hot products of combustion are forced through a liquid or liquid-solid mixture to heat the liquid or liquid-solid mixture. A major advantage of this heating system is that the heat exchange occurs directly between the hot gaseous products of combustion and the liquid. Thus there is no solid interface that interferes with heat exchange. In a submerged combustion system, the hot combustion products a which is typically fuelled by a combination of air and natural gas. The flame generates hot combustion gases which contact the liquid to be heated, but the flame itself does not come into contact with the liquid.
This submerged combustion technology differs from conventional heat exchange methods such as immersion tube heating where the heat exchange is indirect through a solid interface and the products of combustion are exhausted directly to the atmosphere, rather than being forced through the liquid. Submerged combustion can be utilized to heat liquids with overall system efficiency greater than 90%. Conventional hot water boiler indirect heating systems have an efficiency of about 80%. Immersion tube heating systems are relatively low performers and have an efficiency of about 70%.
In applications where separation of components by distillation or absorption is required, submerged combustion heating can be applied to generate liquid or liquid-solid temperatures up to about 195xc2x0 F. This is not much below the boiling point of water, and is applicable to most industrial and domestic liquid or liquid-solids heating applications.
In addition to high efficiency, submerged combustion heating systems are advantageous because they maintain a uniform temperature throughout the liquid in which the submerged combustion is conducted. This is because the hot gaseous combustion products pass rapidly through the liquid and keep the liquid in constant agitation, thereby distributing heat evenly. Submerged combustion heating systems are also suitable for heating contaminated liquids, or liquids with low medium or high solids contents. Expenses are usually lower than with other heating systems because the submerged combustion heating can be conducted in a liquid holding tank which can operate at ambient pressures, thereby eliminating the need to be pressurized. Unlike boiler heating applications, a certified operating engineer is not required to operate a submerged combustion heating system.
Typical industrial applications for submerged combustion systems include: (a) natural gas processing plants for effluent pond heating; (b) municipal effluent holding and treatment ponds - which can include maintenance of pond temperatures to ensure continuous high level of biological degradation especially in regions that experience extreme seasonal temperature changes, and in other cases, elevated temperatures to pasteurize the effluent; (c) aggregate wash plants for heating aggregate wash water at concrete batch plants; (d) log ponds and conditioning chests for heating log ponds and conditioning vats in plywood, veneer, orientated strand board (OSB), waferboard, chopstick plants; (e) pulp and paper for mill water intake protection against freezing, white water solution heating; (f) heap leach mining for heating of barren solutions for ore extraction in heap leaching operations; (g) wet potash mining for heating of barren brine solution to maximize solubility and recovery of potash in flooded potash mines; (h) coal thawing for conveying; (i) carpet and fabric manufacturing for heating of bulk carpet and fabric dyes; (j) cogeneration for evaporation of waste water to recover water treatment chemicals in plants with zero effluent discharge; and (k) industrial processesxe2x80x94processes requiring large volumes of hot water or non-flammable liquids, or processes requiring a direct source of heat for distillation or absorption.
Typical commercial applications for submerged combustion systems include: (a) swimming pool heatingxe2x80x94institutional and residential; (b) fish hatcheriesxe2x80x94fresh water heating; (c) commercial laundriesxe2x80x94wash water heating; (d) automotive car washes; (e) snow disposal; (f) food processing plants, and municipal waste disposal systems.
The applicant is the assignee of one or more of the inventors herein and therefore the owner of the following patents relating to a submerged combustion heating system:
1. U.S. Pat. No. 5,606,965, granted Mar. 4, 1997 entitled xe2x80x9cSubmerged Combustion Systemxe2x80x9d;
2. U.S. Pat. No. 5,615,668, granted Apr. 1, 1997, entitled xe2x80x9cApparatus for Cooling Combustion Chamber in a Submerged Combustion Heating Systemxe2x80x9d; and
3. U.S. Pat. No. 5,636,623, granted Jun. 10, 1997, entitled xe2x80x9cMethod and Apparatus for Minimizing Turbulence in a Submerged Combustion Systemxe2x80x9d.
4. U.S. Pat. No. 5,032,230, Sheppard, discloses a secondary heat recovery system using vacuum.
The subject matter and contents of these three aforementioned U.S. patents is incorporated herein by reference.
The invention is directed to a submerged combustion heating system comprising: (a) a first liquid holding vessel, said first holding vessel having a liquid inlet and a liquid outlet, and an exhaust gas outlet; (b) a combustion chamber positioned in the interior of the first vessel, at least the bottom portion of the combustion chamber being located below the top elevation of the vessel and in the liquid in the first tank; (c) fuel and air conveyors associated with the combustion chamber for conveying fuel and air into the interior of the combustion chamber, said fuel and air being ignited to create a combustion flame inside the combustion chamber, said flame not touching the interior walls of the combustion chamber or the liquid, said flame generating a hot combustion gas; (d) a plurality of openings located in the combustion chamber for enabling the hot combustion gas to be exhausted from the interior of the combustion chamber into liquid in the first vessel below the level of liquid in the first vessel and heating the liquid in the first vessel; (e) a second liquid holding vessel connected to the first vessel and holding liquid; (f) a hot air chamber positioned in the interior of the second liquid vessel and connected with the first vessel, said hot air chamber being connected to and receiving hot combustion gas from the first vessel and exhausting the hot combustion gas through the liquid in the liquid in the second liquid holding vessel and heating the liquid in the second vessel.
The submerged combustion heating system can include a first liquid level control for controlling level of liquid in the first holding vessel so that the level of the top of the liquid is above the plurality of openings in the combustion chamber, and above the liquid inlet but at or below the level of the liquid outlet, and a liquid level control for controlling level of liquid in the second holding vessel, said hot combustion gas transferring heat from the hot combustion gas to the liquid in the first vessel and the liquid in the second vessel. A weir can prevent hot combustion gas from exiting the first vessel through the liquid outlet.
The plurality of openings can be located in the lower region of the combustion chamber and horizontally encircle the periphery of the combustion chamber.
The first vessel can be a hollow cylindrical vessel, having vertical walls, a first bottom, a first top and a first vertical longitudinal axis, and the combustion chamber can be a smaller hollow cylindrical vessel which can have vertical walls, a second bottom, a second top, a second vertical longitudinal axis coincident to the first longitudinal axis of the first cylindrical vessel, and the plurality of openings is located in the lower region of the smaller cylindrical vessel. The top portion of the smaller cylindrical vessel can have a truncated conical shape. The openings can be vertical slots in the lower region of the combustion chamber.
Liquid level in the first vessel can be maintained at a level above the first bottom of the first vessel and above the bottom of the smaller cylindrical vessel and the plurality of openings in the smaller cylindrical vessel, but below the first top of the first vessel, and the portion of the smaller cylindrical vessel comprising the truncated conical shape, the exterior surface of the truncated conical shape portion of the second cylindrical vessel being cooled by wave action created in the liquid in the first vessel by hot combustion gas bubbles generated in the smaller cylindrical vessel and exiting from the plurality of openings and rising to the surface of the liquid being heated in the first vessel; and the level of liquid in the second holding vessel can be maintained at a level above the bottom of the second holding vessel and the hot air chamber, the hot combustion gas from the hot air chamber passing through and heating the liquid in the second vessel.
The combustion chamber can be enclosed by a jacket and hot combustion gas from the combustion chamber openings can pass through the liquid in the first vessel between the combustion chamber and the jacket.
The fuel and air conveyors can convey the fuel and air to a nozzle which can combine the fuel and air for combustion, said nozzle being positioned above the top interior of the combustion chamber. The smaller cylindrical vessel comprising the combustion chamber can have an open bottom.
The second liquid holding vessel can have a plurality of openings spatially distributed around the bottom circumference of the second liquid holding vessel. The second liquid holding vessel can have a conduit which can introduce hot combustion gas into the second liquid holding vessel and the conduit can have a cap thereon which can force the hot combustion gas to pass through the liquid in the secondary holding vessel. The liquid in the second holding vessel can be liquid obtained from the first liquid holding vessel.
The liquid to be heated can be introduced to the second holding vessel and can then pass from the second holding vessel to the first liquid holding vessel with the combustion chamber. The hot combustion gas from the first liquid holding vessel can be passed to the hot air chamber in the second liquid holding vessel.
The submerged combustion system can include a computer which can sense the temperature of the exhaust gas, and the temperatures of the cold liquid being introduced into the first vessel or the second vessel, and the temperatures of the heated liquid being conveyed from one liquid holding vessel to the other, and the temperature of hot liquid being withdrawn from the first or second liquid holding vessel, and can prompt appropriate valves to open when the temperature of the exhaust gas is higher than the temperature of the hot liquid being withdrawn from the first or second liquid holding vessels and can prompt the appropriate valves to close when the temperature of the exhaust gas is the same as the temperature of the hot liquid being withdrawn from the system.
The jacket surrounding the combustion chamber can be in the shape of a hollow cylinder. The jacket can be tapered in an upwardly direction.